High vacuum pump apparatus



Dec. 26, 1967 J. H. BURTHE 3,360,137

HIGH VACUUM PUMP APPARATUS Filed June 4, 1965 5 Sheets-Sheet l E 1"; K5 i I I & II i :k

INVENTOR;

JACK H. BURTHE ATTORNEYS Dec. 26, 1967 J. H. BURTHE HIGH VACUUM PUMP APPARATUS 5 Sheets-Sheet Filed June 1, 1965 INVENTOR. JACK H. BURTHE ATTORNEYS Dec. 26, 1967 J. H. BURTHE 3,360,187

HIGH VACUUM PUMP APPARATUS Filed June 1965 5 Sheets-Sheet 3 Q POWER o T SUPPLY -POWER SUPPLY 4 C83 86 72 L87 I I Hh p I k I \Xi m l8 73 L:

j 74 z \j 82 7I f f i 88 4 i i i x Z 5 78 3 lies i 1 H K [T I r a l E 5 l 9| I INVENTOR. JACK H. BURTHE ATTORNEYS United States Patent 3,360,187 HIGH VACUUM PUMP APPARATUS Jack H. Bur-the, Mountain View, Calif., assignor, by mesne assignments, to The Perkin-Elmer Corporation, Norwalk, Conn., a corporation of New York Filed June 4, 1965, Ser. No. 461,427 7 Claims. (Cl. 230-69) ABSTRACT OF THE DISCLOSURE A high vacuum pump apparatus wherein a bulk quantity of getter material is fed as a rigid body to be evaporated by electron bombardment by advancing and retreating movements of an exteriorly located handle. Electron filaments are shielded from evaporated getter material. The bulk charge of getter material, as moved variously into and out of the bombardment zone created by the filament varies the sublimation pattern within the pumping region. A shield around the charge of getter material defines the vista of exposure of the charge to the shower of electrons within the bombardment field.

This invention relates to high vacuum pump apparatus, and more particularly, to high vacuum pumps employing devices for sublimating getter material particularly in sizeable bulk quantities.

As is known, getter material can be sublirnated by resistance heating techniques wherein a relatively large current is passed through the getter material heating it until it evaporates.

In order to sublimate large amounts of getter material by resistance heating over extended time periods of operation, various arrangements have been employed, usually characterized by bulky reels of getter wire and complex mechanisms to feed the wire. The larger the wire diameter, the greater will be the power required and, therefore, resistance heating has been limited, in general, to smaller diameter wire.

Another technique to evaporate bulk quantities of getter material uses a crucible wherein an electron beam is focused upon the getter material to melt it down. These crucible techniques are characterized by bulky cooling arrangements and are limited to being positioned upright so as to retain the molten metal. To provide a focused beam, various arrangements have been used, ordinarily including magnets and the like. Further, in these crucible techniques the shadow of the lip of the crucible is limiting.

According to the apparatus disclosed herein, the foregoing and other undesirable characteristics have been eliminated, and an improved sublimating pump construction provided.

It is, therefore, a general object of this invention to provide an improved vacuum pump construction employing improved bulk sublimating apparatus.

Another object of the invention is to provide sublimating apparatus including means for projecting a large diameter charge of getter material into and out of an electron diffusion pattern whereby self-supporting rigid getter material is maintained self-supporting while being sublimated in bulk quantities into a vacuum system.

Yet another object is to provide a bulk sublimator having extended life characteristics.

A still further object of the invention is to provide, in a high vacuum apparatus, a bulk sublimator apparatus which projects getter material therefrom forwardly and over an enlarged vista.

These and other objects of the invention will become more clearly apparent from the following detailed description of a preferred embodiment of the invention, when taken in conjunction with the drawings in which:

3,360,187 Patented Dec. 26, 1967 FIGURE 1 is an elevation section view of the upper half of apparatus according to the invention, the section being taken on the longitudinal center line thereof, and showing a charge of getter material disposed in its advanced position;

FIGURE 2 is a longitudinal center line section view of the lower half of the apparatus in FIGURE 1 showing a charge of getter material in its retracted position;

FIGURE 3 is an end view of apparatus shown in FIG- URES 1 and 2 and taken on a line 33 thereof;

FIGURE 4 is an enlarged detail view of a central portion of FIGURE 3;

FIGURE 5 is an end sectional line 5-5 of FIGURES 1 and 2;

FIGURE 6 is an enlarged detail view partially in section showing electrical connection as made to the charge of getter material;

FIGURE 7 is a vertical centerline view partially in section schematically showing a pump assembly incorporating the sublimator apparatus according to FIGURES 1 through 6; and

FIGURE 8 is an enlarged detail view in perspective of a portion of a filament assembly as disclosed herein.

High vacuum pumping apparatus for use in a high vacuum system has been provided herein which, in general, is characterized by the sublimator apparatus thereof. Means are provided for supporting an elongated rigid charge of getter material for movement between advanced and retracted positions on its axis. An electron source is formed which emits a diffusion pattern of electrons from positions disposed around the axis of movement of the charge of getter material. The diffusion pattern forms a bombardment zone into which the inner end of the charge of getter material can be projected to be Sublimated. Thus, by applying a sufficiently high positive potential to the rigid charge with respect to the electron emission source, electrons will flow from the source to sublimate the charge material into the vacuum system and thereby trap gas therein.

As more particularly shown in the drawings, a base plate 10 is adapted to form a closure for an access opening into a high vacuum enclosure, as by the bolt holes 11 through the outer periphery of base plate 10. A sealing surface, such as rib 12, is adapted to cooperate with a conventional sealing gasket.

Means are provided for supporting a relatively large diameter, elongated charge 13 of getter material, such as titanium, for movement between advanced and retracted positions whereby the charge 13 can be projected into and out of a diifusion pattern of electrons serving to sublimate the material of charge 13.

Thus, base plate 10 is formed with an opening 14 adapted to receive a threaded bushing 16. A plunger assembly extends through base plate 10 and is operable by means of the elongated threaded stem or control rod 17 which is adapted to be screwed in opposite directions through bushing 16. A handle or knob 18 is carried on the outer end of control rod 17.

Rotational movement applied to rod 17 is converted to a straight axial thrust applied to charge 13 by means of a thrust bearing 19. Bearing 19 includes an inner and an outer race 21 and 22, respectively. Race 21 is retained fixed to rotate with the inner end of rod 17. Race 22, on the other hand, serves to support an imperforate cap member 23 which thereby moves axially with axial movement of control rod 17.

An imperforate bellows 24 is arranged coaxially of the inner end of rod 17 and is sealed at one end to cap member 23. The other end of bellows 24 is sealed to an annular boss 26, formed on the inside face of base member 10. A vent 27 forms a small air passage between the outview taken along the side atmosphere and the space within bellows 24. Thus, as bellows 24 becomes elongated with inward movement of control rod 17, atmospheric pressure will remain within bellows 24.

Cap member 23 includes a flange portion 23a, formed around the periphery, which is adapted to support in insulated relation an annular seat member 28. Member 28 includes a cylindrical annular seat 29 adapted to receive one end of charge 13.

Charge 13 includes a groove 31 encircling that end adapted to be retained in seat 29. Three retaining pins 32 are threaded radially through seat member 28 to cooperate with groove 31 and thereby positively and firmly engage charge 13 to retain it for movement along its own axis 33. In order to insulate cap member 23 from seat member 28, conventional ceramic insulator assemblies 34 are provided Which include inner and outer shields 36, 37, and a ceramic insulator 38 held by screws.

Electron emission means for diffusing electrons from positions distributed around the axis 33 of charge 13 provides a bombardment zone adapted to surround the charge 13 during sublimation.

More particularly, a filament support plate 41 is mounted upon four support rods 42 fixed to the inner face of base plate 10 so as to dispose plate 41 substantially normal to axis 33. This disposition of plate 41 permits it to serve as a protective shield for components located between plate 41 and base plate 10*, whereby such components are protected from receiving a surface application of getter material.

As shown in the drawing, eight tungsten filaments 43 are distributed around axis 33 and spaced equidistant therefrom for purposes of emitting a ditfused pattern of electrons for bombarding the surface of charge 13. Each filament 43 is supported in a filament assembly 44 carried by filament support plate 41. The plurality of filaments 43 are spaced sufficiently laterally of axis 33 to provide a diffused pattern of electron adapted to surround the periphery of one end of charge 13, A protective shield 46 forms part of the support, but more importantly, is positionally associated for shielding each filament and precluding alloying between the getter material and the tungsten filaments which traditionally has foreshortened the life of sublimating apparatus. Each shield 46 is disposed between its associated filament and axis 33 and lies across that plane 50 (FIG. which includes both the associated filament and the axis as to be adapted to intercept evaporated getter material traveling toward the filament from the charge. In short, shields 46 serve to provide line-of-sight shielding for the elongated tungsten filaments 43, whereby the latter are protected from the deleterious effects of impinging getter material.

As thus arranged, filaments 43 and their associated shields 46 are disposed coaxially of axis 33. A typical width for shields 46 can run on the order of threesixteenths of an inch to an eighth of an inch, so as to subtend a relatively narrow angle from the axis of its associated filament 43, whereby the diffused electron patterns provided by filaments 43 shall not be significantly reduced.

Means are provided adapted to apply a suitable potential to each filament 43 whereby the filament will operate at a temperature just under 2500 degrees Kelvin, and, preferably, on the order of 2400 degrees Kelvin, as in a typical example employing 43 amperes alternating current at 4.5 volts.

Electrical connection is made to filaments 43 by means of a conventional lead-through conductor device 47 provided with a conventional terminal tip 48 extending outside the vacuum enclosure. The inner end of each lead through device 47 is carried in one of several holes 49 in an insulator disc 51 which itself is carried on the ends of support rods 42. An annular protective plate 40 is carried by support rods 42 spaced closely to insulating disc 51 so as to protect against the deposit of a short circuiting layer of getter upon disc 51. Spacers 55 and 60 of stainless steel are employed to obtain clearances. Each lead-through device 47 passes through an opening in plate 41 and carries an associated conductor bar 52 which is attached to extend between lead-through conductor devices 47 and an associated one of the emitter assemblies 44. One end of a U-shaped mounting post 53 contacts conductor bar 52 and the other end supports an end of tungsten filament 43. The other end of filament 43 is supported by the forwardly turned lip 46:: of shield 46. Ceramic insulators 54, 56 are provided for support of shield 46 and post 53.

A sufficiently high positive potential is applied to the getter charge 13, for example, on the order of 6 kilovolts DC, with respect to the electron emission source to cause electrons from filaments 43 to sublimate the material of charge 13.

Thus, an electrical connector assembly includes a conventional high vacuum lead-through conductor 57 having a tip 58 extending through base plate 10 for connection with a suitable direct current source. The inner end of a lead-through conductor 57 carries a conductive cable 59. Cable 59 is electrically connected by means of the screw 65 to seat member 28. Seat member 28, it will be recalled, is supported in insulated relation with respect to the plunger assembly, but makes direct contact with the proximate end of charge 13 whereby charge 13 can be biased to a suitable relatively high positive potential. The distal end of charge 13 is positionable to be exposed to the electron diffusion pattern of filaments 43.

Thus, as previously mentioned, the electron emitting filaments 43 provide diffusion of electrons from positions distributed around axis 33 of charge 13 so as to provide a bombardment zone 61 including a diffused pattern of electrons adapted to surround the distal end of the charge of getter.

Means are provided for forming a delimiting protective boundary to the bombardment zone 61 which further provides a forwardly projected sublimation of getter material over an enlarged vista.

Thus, a cylindrical conductive sleeve 62 of suitable material, such as tantalum, is supported coaxially of axis 33 in protective relation to charge 13, whereby, in general, only a protruding end portion of charge 13 will be disposed into bombardment zone 61. The remainder of the charge will, therefore, remain somewhat cooler and maintain its self-supporting rigidity. Sleeve 62 is supported by an annular skirt 63 which encircles it and is attached, as by screws, to filament support plate 41.

As can be seen in the drawing, as the distal end of charge 13 protrudes further and further out of sleeve 62 it is subjected to electron bombardment by the diffused pattern of electrons over an increasingly enlarging vista. For example, as defined by the limit lines 64, an angle of sublimation exposure of 270 degrees is subtended within which getter can escape into the vacuum system. As the charge 13 is fed further beyond the inner end of cylinder 62 an even greater angle of sublimation exposure is provided, as indicated by the limit lines 66. As can be seen from lines 66, the maximum vista exposed is limited by the angle subtended from the periphcry of filament support plate 41 and the furthest remote points on axis 33 still within range of the electron diffusion pattern provided by filaments 43. The minimum is defined by the edge 67 of the inner open end of cylinder 62 whereby when charge 13 is retracted sufiiciently, it will lie within the protective shadow of edge 67.

It has been observed that the boundary of the bombardment zone can be selectively moved axially of charge 13 by varying the potential applied to sleeve 62. Ground potential, indicated at 68, serves to dispose the boundary at an associated position along axis 33 which is suitable for most purposes. However, under certain circumof the diffused stances it may be desired to advance or retract the boundary along axis 33 and for this purpose, suitable electric connections can be made to sleeve 62, as desired.

A vacuum system as shown in FIGURE 7 includes a cylindrical enclosure 71 which defines a portion of the volume of gas to be pumped. Enclosure 71 as sealed at its upper end as shown by a plate 72, which, for example, can be bolted to a flange 73 formed around the upper end of enclosure 71. Plate 72 supports an access well formed by a coaxial cylinder 74 and a flanged boss portion 76. Centrally of boss 76, an access opening 77 is formed and adapted to accommodate the entry of a sublimator assembly 78 of a type corresponding to that described above. Sublimator assembly 78, therefore, includes base plate which is bolted in high vacuum sealing relation to the flange 79 formed on the upper end of boss portion 76.

As thus arranged, rotational movement of handle 18 serves to advance and retract the charge of getter material into and out of bombardment zone 61 of the sublimator. A protective cover plate 81 is positioned to close the well formed by cylinder 74.

A typical high vacuum system application, as shown in FIGURE 7, equipped to pump inert gas will customarily also include a plurality of encircling magnets 82, surrounding enclosure 71, for coacting with a suitable ion pump (not shown). Magnets 82 are connected to a power supply 83 via a meter 84. Permanent magnets can, of course, be substituted for the electromagnets 82 shown in FIGURE 7. A power supply 86 is also shown connected through a meter 87 to the tip 48 of leadthrough device 47 for heating the thermionic tungsten filaments 43.

Means are provided in the form of a stainless steel mesh screen 88 coaxially supported about axis 33 between the inside wall of enclosure 71 and the sublimator assembly 78, for purposes of removing meter reading errors which have been observed to be otherwise present in the system.

Screen 88 is grounded as schematically indicated by the representation at 89'.

The vacuum pump assembly, which includes magnets 82, enclosure 71, and sublimator assembly 78, is attached, as by bolts, to the flange 91 of a chamber 92, or tank, to be pumped.

Operation of the sublimator or pump apparatus is as follows:

Power supply 86 is adjusted to bring the temperature of tungsten filaments 43 to a temperature on the order of 2400 degrees Kelvin. With the tungsten degrees at this temperature, the end of charge 13, when exposed into the bombardment zone 61 will be Sublimated, but at a temperature insufiicient to destroy the self-supporting rigidity of the getter charge.

In short, it is intended that the apparatus will be operated at a temperature which permits sublimation but which does not encounter a general melting down of the titanlum material.

Accordingly, shield 62 serves to limit the application electron bombardment to the exposed end portion of charge 13 while the remainder of the charge is free from electron attack. Nob 18, when rotated in one direction, threads rod 17 into the vacuum system to advance charge 13 into bombardment zone 61. Rotation in the opposite direction retracts the charge. By varying the exposure of the end of charge 13, sublimation can be varied.

In the operation of the above pump apparatus, it is intended that getter material can be sublirnated in bulk quantities at a rate on the order of 1 gram per hour extending over a period of at least one hundred hours. When operating the equipment at a lower sublimation rate, the apparatus can perform for more extended periods, on the order of ten thousand hours.

As getter material evaporates from the end of charge 13 it is precluded by shields 46 from alloying with the tungsten filaments 43, thereby considerably extending the filament life to permit operation to continue for the long periods noted above.

By successfully extending the filament life by several orders of magnitude, the life of the pump in a vacuum system has been commensurately extended. This is generally the determining factor in the installed life of most pump assemblies. To replace filaments normally entails a loss of vacuum, since the sublimator apparatus would have to be removed from the vacuum system.

In the operation of the apparatus, the eight filaments 43 are normally operated in sets of four each, rather than to employ all eight at the same time. This further serves to provide sublimation over a still greater period of time.

Thus, it should be readily apparent that there has been provided a bulk sublimator apparatus whose surface area is quite large and subjected to diffused electron bombardment sufiicient to give a relatively high sublimation rate. For example, a rate on the order of one gram per hour can be continued for a period of one hundred hours or more, without entailing significant melting of the gettering charge.

The tungsten filaments provide a difiused pattern of electron emission and are protected against deleterious alloying with the gettering material so that their life is significantly extended. Accordingly, the overall life of the pump, when installed in a given system, will be commensurately extended and can remain in place in the vacuum system for long periods.

The current requirements of a commensurating resistance heating style of sublimator and the necessarily attendant cooling apparatus is obviated.

Great quantities of getter material, such as titanium, can be evaporated from the charge. For example, using a 600-gram charge as supported herein will permit as much as 400 grams of the charge to be Sublimated. A supply of the evaporant on this order can serve for many hours of operation before it is exhausted. Furthermore, the degree of consumption of the charge is subject to being controlled between very wide limits by virtue of the plunger mechanism for advancing the evaporant into and out of the bombardment zone and by closely defining the boundary of the zone.

It will, of course, be readily apparent, as compared to bulk sublimators employing crucibles for containing molten evaporant, that the above described sublimator assembly can be operated in any position. Large quantities of evaporant can be used without having to introduce "bulky reels of wire and their associated driving mechanisms. The plunger mechanism described above, in accordance with the present apparatus, is obviously of extremely simple construction and of limited expense while providing control of the positioning movements of the charge from outside the vacuum enclosure.

By limiting the difi'used shower of electrons to grazing trajectories the filament performance is extended.

Finally, the angle of sublimation provides a broadened vista for projection of the evaporated getter material.

I claim:

1. In a high vacuum system, pump apparatus for sublimating an elongated rigid charge of getter material, said apparatus comprising means for supporting an elongated rigid charge of getter material on a predetermined axis within the vacuum system, means forming an electron source disposed laterally of and around the axis of the charge and adapted to bombard an end portion of the charge with a diffused application of electrons, means operatively coupled to move the first named means to dispose the inner end of said charge variously within the shower of into and out of range of the bombarding electrons to sublimate the material of the charge, and means adapted to apply a sufiiciently high positive potential to the charge with respect to said source to cause electrons from the source to sublimate the charge material into the vacuum system to trap gas.

2. In a high vacuum system, pump apparatus for sublimating an elongated rigid charge of getter material oomprising means adapted to engage one end of an elongated rigid charge of getter material and support the charge on a predetermined axis within the vacuum system, electron source means for emitting a diffused pattern of electrons from positions laterally of and disposed around said axis at a predetermined axial disposition therealong, means cooperating with the first named means for moving the other end of the charge between retracted and advanced positions out of and variously into said pattern to subject said other end to diffused electron bombardment and serving to vary the projection of the Sublimated getter material from the charge, and means adapted to apply a sufficiently high positive potential to the charge with respect to said source to cause electrons from the source to sublimate the charge material into the vacuum system to trap gas.

3. In a high vacuum system, pump apparatus for sublimating an elongated rigid charge of getter material comprising means adapted to engage one end of an elongated rigid charge of getter material and support the charge on a predetermined axis Within the vacuum system, a plurality of electron emitting filaments disposed around and spaced sufiiciently laterally of said axis to provide a diffused pattern of electrons adapted to surround the periphery of the other end of the charge, a protective shield positionally associated with each filament, each shield being disposed between its associated filament and said axis, and disposed in that plane which includes both the associated filament and said axis so as to be adapted to intercept evaporated getter material traveling toward the filament from the charge, means cooperating with the first named means for moving said other end of the charge between retracted and advanced positions, respectively, out of and into said pattern to subject said other end to diffused electron bombardment, and means adapted to apply a sufiiciently high positive potential to the charge with respect to said filaments to cause electrons from the filaments to sublimate the charge material into the vacuum system to trap gas therein.

4. In a high vacuum system, pump apparatus for sublimating an elongated rigid charge of getter material comprising means adapted to engage one end of an elongated rigid charge of getter material and support the charge on a predetermined axis within the vacuum system, electron emission means for diffusing electrons from positions distributed around said axis to provide a bombardment zone adapted to surround the distal end of the charge when sublimating same, a cylindrical sleeve and means supporting same coaxially of said axis to delimit one boundary of said zone, means for applying a predetermined electric potential to said sleeve to dispose said boundary at an associated position along said axis, means for moving the first named means between retracted and projected positions for advancing a charge into said bombardment zone, and means adapted to apply a sufficiently high positive potential to the charge with respect to said electron emission means to cause electrons from the emission means to sublimate the charge material into the vacuum system to trap gas therein.

5. In a high vacuum system including an enclosure defining a volume of gas to be pumped, wherein the enclosure includes an opening adapted to receive a pump assembly Within the enclosure, apparatus comprising base means adapted to form a closure for said opening, a plunger passing through said base means, a thrust bearing on that end of the plunger adapted to be disposed within the enclosure, said bearing having inner and outer races, the inner race being rotationally movable with respect to the outer race, an imperforate cap member carried by the outer race to move axially With the plunger, means forming an elongatable vacuum seal extending between said cap member and said base means, means supported and carried by the cap member and forming a seat adapted to receive one end of an elongated rigid charge of getter material and to retain said charge on a predetermined axis, electron emission means for difiusing electrons from positions distributed around said axis to provide a bombardment zone adapted to surround the other end of the charge when sublimating same, a cylindrical sleeve and means supporting same coaxially of said axis, one end of said sleeve opening into said bombardment zone, the other end being adapted to receive the charge retained in said seat, means for moving said plunger between retracted and advanced positions to project a charge through said sleeve respectively out of and into said bombardment zone, and means adapted to apply a sufiiciently high voltage between the charge and said emission means to sublimate the charge material by electron bombardment thereof.

6. Apparatus according to claim 5 further including a conductive perforate cylindrical sleeve coaxially disposed about said axis and lying between said electron emitting positions and said enclosure, and means adapted to maintain said perforate sleeve at ground potential.

7. In a high vacuum system, enclosure means defining a volume to be pumped, pump apparatus for sublimating an elongated rigid charge of getter material of a predetermined length, said apparatus comprising support means within the enclosure adapted to engage one end of the charge and support the charge on a predetermined axis within the system, electron source means forming an elec' tron bombardment zone around the axis and adapted to cause a diffused shower of electrons to graze the periphery of the other end of the charge to sublimate the material thereof, means outside the enclosure coupled to move the support means between retracted and advanced positions to selectively and variously expose said other end of the charge to said shower of electrons to vary the vista of sublimation of material therefrom, extensible means between said support means and the last named means serving to form a high vacuum seal therebetween; and means adapted to apply a sufliciently high positive potential to the charge with respect to said electron source means to cause electrons from the source to sublimate the charge material into the vacuum system to trap gas.

References Cited UNITED STATES PATENTS ROBERT M. WALKER, Primary Examiner. 

1. IN A HIGH VACUUM SYSTEM, PUMP APPARATUS FOR SUBLIMINATING AN ELONGATED RIGID CHARGE OF GETTER MATERIAL, SAID APPARATUS COMPRISING MEANS FOR SUPPORTING AN ELONGATED RIGID CHARGE OF GETTER MATERIAL ON A PREDETERMINED AXIW WITHIN THE VACUUM SYSTEM, MEANS FORMING AN ELECTRON SOURCE DISPOSED LATERALLY OF AN AROUND THE AXIS OF THE CHARGE AND ADAPTED TO BOMBARD AN END PORTION OF THE CHARGE WTH A DIFFUSED APPLICATION OF ELECTRONS, MEANS OPERATIVELY COUPLED TO MOVE THE FIRST NAMED MEANS TO DISPOSE THE INNER END OF SAID CHARGE VARIOUSLY WITHIN THE SHOWER OF INTO AND OUT OF RANGE OF THE BOMBARDING ELECTRONS TO SUBLIMATE THE MATERIAL OF THE CHARGE, AND MEANS ADAPTED TO APPLY A SUFFICIENTLY HIGH POSITIVE POTENTIAL TO THE CHARGE WITH RESPECT TO SAID SOURCE TO CAUSE ELECTRONS FROM THE SOURCE TO SUBLIMATE THE CHARGE MATERIAL INTO THE VACUUM SYSTEM TO TRAP GAS. 